1. Field of the Invention
This invention relates generally to a method for the treatment, for global environmental protection, of a carbon dioxide-containing gas discharged in a large quantity from, for example, thermoelectric power plants and iron mills and, more specifically, to a method for dissolving carbon dioxide in seawater and discharging the carbon dioxide-dissolved seawater to a deep sea level. The present invention is also directed to an apparatus for carrying out the above method.
2. The Prior Art
U.S. Pat. No. 5,662,837 (Saito et al) discloses method and apparatus for dissolving carbon dioxide gas discharged from, for example, thermoelectric power plants into seawater and isolating it at a deep sea level. The apparatus includes an inverted J-shaped gas lift having a shorter pipe and a longer pipe connected with each other at a top of the J-shaped gas lift. The shorter pipe is held at a shallow sea level, while the longer pipe is opened at a deep sea level. When carbon dioxide gas is injected into the lower end of the shorter pipe, the seawater is introduced into the shorter pipe by gas lift action of the carbon dioxide gas. The carbon dioxide fed is completely dissolved into the seawater before it reaches the upper end of the shorter pipe. Because of an increased density of the seawater due to dissolution of carbon dioxide, because of a higher pressure within the upper end than an outside pressure and because of the force of inertia, the seawater is then moved down through the longer pipe and discharged from its lower end located at a deep sea level.
The above technique which does not require liquefaction of CO.sub.2 gas and which ensures environmental protection is promising. However, the known method has a problem because the CO.sub.2, gas to be treated should have a high purity and should not contain gases, such as N.sub.2 and O.sub.2, which are hardly soluble in seawater. Thus, such insoluble gases will be discharged from the end of the long pipe together with the CO.sub.2 -dissolved seawater to form a large amount of bubbles. Thus, prior to the treatment with the above apparatus, the CO.sub.2 gas must be pretreated to obtain a high purity CO.sub.2 gas at a large cost.